<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var username = "张三";
        document.write(username);
        var username2 = '李四';
        document.write(username2);
        document.write('你好,"大家好"')
        document.write("<h2>hello</h2>");
        // 单双引号不可换行 `引号是可以换行
        document.write(`<h1>
            <span>xxxxx</span>
        </h1>`)
    </script>
</body>
</html>